U.S. patent number 9,998,253 [Application Number 15/265,490] was granted by the patent office on 2018-06-12 for use of wavelength selective switch for a few-mode fiber.
This patent grant is currently assigned to Lumentum Operations LLC. The grantee listed for this patent is Lumentum Operations LLC. Invention is credited to Paul Colbourne.
United States Patent |
9,998,253 |
Colbourne |
June 12, 2018 |
Use of wavelength selective switch for a few-mode fiber
Abstract
A wavelength selective switch (WSS) may include a front-end unit
that includes an input few-mode fiber (FMF) providing an input
optical signal including multiple wavelengths. The multiple
wavelengths may each have N modes. The front-end unit may include
two or more output few-mode fibers (FMFs), and a side that has a
1.times.N port for each of the input FMF and the two or more output
FMFs. Each of the 1.times.N ports may be single mode in a
wavelength dispersion dimension and N-mode in a switching
dimension. The WSS may include a switching element to receive the
input optical signal from the front-end unit, switch each of the
multiple wavelengths of the input optical signal to form one or
more output optical signals, and direct each of the one or more
output optical signals to a corresponding 1.times.N port of the
front-end unit.
Inventors: |
Colbourne; Paul (Ottawa,
CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Lumentum Operations LLC |
Milpitas |
CA |
US |
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Assignee: |
Lumentum Operations LLC
(Milpitas, CA)
|
Family
ID: |
58237430 |
Appl.
No.: |
15/265,490 |
Filed: |
September 14, 2016 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20170078040 A1 |
Mar 16, 2017 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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62219431 |
Sep 16, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04Q
11/0066 (20130101); G02B 6/356 (20130101); H04J
14/0212 (20130101); H04Q 11/0005 (20130101); H04B
10/2581 (20130101); G02B 6/14 (20130101); H04J
14/04 (20130101); H04Q 2011/0026 (20130101); G02B
6/3548 (20130101); H04Q 2011/0016 (20130101); G02B
6/3512 (20130101) |
Current International
Class: |
H04J
14/00 (20060101); H04J 14/02 (20060101); G02B
6/35 (20060101); H04B 10/2581 (20130101); G02B
6/14 (20060101); H04Q 11/00 (20060101) |
Field of
Search: |
;398/49 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Fontaine et al., "Few-Mode Fiber Wavelength Selective Switch with
Spatial-Diversity and Reduced-Steering Angle," Optical Society of
America, 2014, 3 pages. cited by applicant .
Labroille et al., "Efficient and mode selective spatial mode
multiplexer based on multi-plane light conversion," Optics Express,
Optical Society of America, vol. 22, No. 13, Jun. 30, 2014, 9
pages. cited by applicant .
Sridharan et al., "Mode-converters for rectangular-core fiber
amplifiers to achieve diffraction-limited power scaling," Optics
Express, Optical Society of America, vol. 20, No. 27, Dec. 17,
2012, 9 pages. cited by applicant.
|
Primary Examiner: Torres; Juan A
Attorney, Agent or Firm: Harrity & Harrity, LLP
Parent Case Text
RELATED APPLICATION
This application claims priority under 35 U.S.C. .sctn. 119 to U.S.
Provisional Patent Application No. 62/219,431, filed on Sep. 16,
2015, the content of which is incorporated by reference herein in
its entirety.
Claims
What is claimed is:
1. A wavelength selective switch (WSS), comprising: a front-end
unit comprising: an input few-mode fiber (FMF) providing an input
optical signal comprising multiple wavelengths, the multiple
wavelengths each having N modes; two or more output few-mode fibers
(FMFs); and a side of the front-end unit having a 1.times.N port
for each of the input FMF and the two or more output FMFs, each of
the 1.times.N ports being single mode in a wavelength dispersion
dimension and N-mode in a switching dimension, the switching
dimension being perpendicular to the wavelength dispersion
dimension, and the switching dimension and the wavelength
dispersion dimension being perpendicular to a direction of
propagation of the input optical signal a height of each 1.times.N
port in the switching dimension being less than
((N-1).times.4.omega.)+2.omega., where .omega. is equal to a mode
radius of a single-mode input with a same numerical aperture; and a
switching element to: receive the input optical signal from the
front-end unit; switch each of the multiple wavelengths of the
input optical signal to form one or more output optical signals;
and direct each of the one or more output optical signals to a
corresponding 1.times.N port of the front-end unit.
2. The WSS of claim 1, where a height of each 1.times.N port in the
switching dimension is approximately equal to
1.3.omega..times.(N-1)+2.omega..
3. The WSS of claim 1, where a width of each 1.times.N port in the
wavelength dispersion dimension is approximately equal to
2.omega..
4. The WSS of claim 1, where the front-end unit comprises mode
converters for each of the input FMF and the two or more output
FMFs, where the side of the front-end unit comprises ends of each
of the mode converters, where each end has a 1.times.N port of the
1.times.N ports.
5. The WSS of claim 4, where each mode converter includes a set of
waveguides, where, along a length of each mode converter, the set
of waveguides merge to form a single rectangular waveguide that
provides the 1.times.N port at the end of the mode converter.
6. The WSS of claim 4, where each mode converter includes a single
waveguide, where, along a length of each mode converter, the single
waveguide is altered to form a waveguide that provides the
1.times.N port.
7. The WSS of claim 4, where each mode converter includes a series
of diffractive elements.
8. A wavelength selective switch (WSS), comprising: a front-end
unit comprising: two or more input few-mode fibers (FMFs) providing
two or more input optical signals, each input optical signal
comprising multiple wavelengths, where the multiple wavelengths
each have N modes; at least one output few-mode fiber (FMF); and a
side of the front-end unit having a 1.times.N port for each of the
two or more input FMFs and the at least one output FMF, each of the
1.times.N ports being single mode in a wavelength dispersion
dimension and N-mode in a switching dimension, a height of each
1.times.N port in the switching dimension being less than
((N-1).times.4.omega.)+2.omega., where .omega. is equal to a mode
radius of a single-mode input with a same numerical aperture; and a
switching element to: receive the two or more input optical signals
from the front-end unit; switch each of the multiple wavelengths of
the two or more input optical signals to form one or more output
optical signals; and direct each of the one or more output optical
signals to a corresponding 1.times.N port of the front-end
unit.
9. The WSS of claim 8, where a height of a 1.times.N port, of the
1.times.N ports, is approximately equal to
1.3.omega..times.(N-1)+2.omega..
10. The WSS of claim 8, where a width of a 1.times.N port, of the
1.times.N ports, is approximately equal to 2.omega., where the
width is in the wavelength dispersion dimension.
11. The WSS of claim 8, where the front-end unit comprises mode
converters for each of the two or more input FMFs and the at least
one output FMF, where the side of the front-end unit comprises ends
of each of the mode converters, where each end has a 1.times.N port
of the 1.times.N ports.
12. The WSS of claim 8, where a distance between a first 1.times.N
port, associated with an input FMF of the two or more input FMFs,
and a second 1.times.N port, associated with an output FMF of the
at least one output FMF, is greater than or equal to approximately
three times a mode radius of a single-mode input with a same
numerical aperture.
13. The WSS of claim 11, where a mode converter, of the mode
converters, includes a set of waveguides, where, along a length of
the mode converter, the set of waveguides merge to form a single
rectangular waveguide that provides the 1.times.N port at the end
of the mode converter.
14. The WSS of claim 11, where a mode converter, of the mode
converters, includes a single waveguide, where, along a length of
the mode converter, the single waveguide is altered to form a
waveguide that provides the 1.times.N port.
15. A wavelength selective switch (WSS), comprising: a front-end
unit comprising: an input fiber providing an input optical signal
comprising multiple wavelengths, where the multiple wavelengths
each have N modes; at least two output fibers; and the front-end
unit having a 1.times.N port for each of the input fiber and the at
least two output fibers, each of the 1.times.N ports being single
mode in a wavelength dispersion dimension and N-mode in a switching
dimension a height of each 1.times.N port in the switching
dimension being less than ((N-1).times.4.omega.)+2.omega., where
.omega. is equal to a mode radius of a single-mode input with a
same numerical aperture; and a switching element to: receive the
input optical signal from the front-end unit; switch each of the
multiple wavelengths of the input optical signal to form one or
more output optical signals; and direct each of the one or more
output optical signals to a corresponding 1.times.N port.
16. The WSS of claim 15, where the input fiber and the at least two
output fibers are few-mode fibers.
17. The WSS of claim 15, where a height of a 1.times.N port, of the
1.times.N ports, in the switching dimension is approximately equal
to 1.3.omega..times.(N-1)+2.omega..
18. The WSS of claim 15, where a width of a 1.times.N port, of the
1.times.N ports, in the wavelength dispersion dimension is
approximately equal to 2.omega..
19. The WSS of claim 15, where the front-end unit comprises mode
converters for each of the input fiber and the at least two output
fibers, where each of the mode converters has a 1.times.N port of
the 1.times.N ports.
20. The WSS of claim 19, where at least one mode converter, of the
mode converters, includes one or more waveguides or a series of
diffractive elements.
Description
TECHNICAL FIELD
The present disclosure relates to a wavelength selective switch
(WSS) and, more particularly, to a WSS for use with a few-mode
fiber (FMF), where a mode structure, associated with modes of the
FMF, are single-mode in a first dimension and multi-mode in a
second dimension.
BACKGROUND
In an optical communication network, optical signals, having
optical channels centered around individual wavelengths (sometimes
referred to as "wavelength channels"), may be transmitted from one
location to another through a length of an optical fiber, such as a
single-mode fiber (SMF). An optical cross-connect module may allow
for switching of optical signals from one optical fiber to another
optical fiber. Similarly, a wavelength-selective optical
cross-connect (herein referred to as a "wavelength selective
switch" (WSS)) may provide for reconfigurable wavelength-dependent
switching between optical fibers. In other words, the WSS may allow
one or more first wavelength channels to be switched from a first
optical fiber to a second optical fiber, while permitting one or
more second (i.e., different) wavelength channels to propagate in
the second optical fiber or to be switched to a third optical
fiber. In a typical scenario, the WSS may be configured to switch
wavelength channels between one or more input optical fibers and a
group (e.g., four, eight, ten, twenty, etc.) output optical
fibers.
SUMMARY
According to some possible implementations, a wavelength selective
switch (WSS) may include: a front-end unit comprising: an input
few-mode fiber (FMF) providing an input optical signal comprising
multiple wavelengths, where the multiple wavelengths each have N
modes; two or more output few-mode fibers (FMFs); and a side of the
front-end unit that has a 1.times.N port for each of the input FMF
and the two or more output FMFs, where each of the 1.times.N ports
may be single mode in a wavelength dispersion dimension and N-mode
in a switching dimension, where the switching dimension may be
perpendicular to the wavelength dispersion dimension, and the
switching dimension and the wavelength dispersion dimension may be
perpendicular to a direction of propagation of the input optical
signal; and a switching element to: receive the input optical
signal from the front-end unit; switch each of the multiple
wavelengths of the input optical signal to form one or more output
optical signals; and direct each of the one or more output optical
signals to a corresponding 1.times.N port of the front-end
unit.
According to some possible implementations, a wavelength selective
switch (WSS) may include: a front-end unit comprising: two or more
input few-mode fibers (FMFs) providing two or more input optical
signals, where each input optical signal may comprise multiple
wavelengths, where the multiple wavelengths each has N modes; at
least one output few-mode fiber (FMF); and a side of the front-end
unit having a 1.times.N port for each of the two or more input FMFs
and the at least one output FMF, where each of the 1.times.N ports
may be single mode in a wavelength dispersion dimension and N-mode
in a switching dimension; and a switching element to: receive the
two or more input optical signals from the front-end unit; switch
each of the multiple wavelengths of the two or more input optical
signals to form one or more output optical signals; and direct each
of the one or more output optical signals to a corresponding
1.times.N port of the front-end unit.
According to some possible implementations, a wavelength selective
switch (WSS) may include: a front-end unit comprising: an input
fiber providing an input optical signal comprising multiple
wavelengths, where the multiple wavelengths each has N modes; at
least two output fibers; and the front-end unit having a 1.times.N
port for each of the input fiber and the at least two output
fibers, where each of the 1.times.N ports may be single mode in a
wavelength dispersion dimension and N-mode in a switching
dimension; and a switching element to: receive the input optical
signal from the front-end unit; switch each of the multiple
wavelengths of the input optical signal to form one or more output
optical signals; and direct each of the one or more output optical
signals to a corresponding 1.times.N port.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram of a prior wavelength selective switch designed
to reduce degradation of spectral resolution when using few-mode
fiber;
FIGS. 2A-2C are diagrams of example wavelength selective switches,
for use with few-mode fiber, that provide decreased degradation of
spectral resolution while allowing for a reduced switching angle
requirement and/or a reduced optics height;
FIG. 3 is a diagram of example components of a wavelength selective
switch, for use the few-mode fiber, as described with regard to
FIGS. 2A-2C; and
FIG. 4 is a diagram of an example environment in which systems
and/or methods described herein may be implemented.
DETAILED DESCRIPTION
The following detailed description of example implementations
refers to the accompanying drawings. The same reference numbers in
different drawings may identify the same or similar elements. The
implementations described below are merely examples and are not
intended to limit the implementations to the precise forms
disclosed. Instead, the implementations were selected for
description to enable one of ordinary skill in the art to practice
the implementations.
In some cases, it may be desirable to use a few-mode fiber (FMF)
with a WSS. A FMF is an optical fiber that supports N modes
(50.gtoreq.N>1, N Integer), where the number of N modes is more
than the one spatial mode (e.g., a pathway for an optical signal
within an optical fiber) supported by a SMF, but fewer spatial
modes than a typical number of spatial modes supported by a
larger-core multi-mode fiber. For example, in some implementations,
the FMF may support approximately two to 50 spatial modes, while
three, six, and ten modes are typical for circular core FMF.
Alternatively, 20 or less modes may be typical for rectangular core
FMF. In some cases, it may be desirable to use FMFs for
transmission of information since information can be encoded on
each of the modes, thus increasing the fiber transmission capacity
as compared to a SMF.
However, when using a FMF with a WSS, wavelength degradation may
become problematic. For example, using the FMF with the WSS may
result in degradation of spectral resolution since different modes
propagating in the FMF have different physical positions within the
FMF core, and a change in physical position in the wavelength
dispersion direction of the WSS will result in a wavelength shift
of the spectral response, and hence a change in the passband edge
locations. The different possible passband edge locations (i.e., a
range of possible passband edge locations) cause a reduction in a
clear channel passband, associated with each channel, within which
information may be transmitted. In other words, use of FMF with the
WSS may reduce an amount of usable bandwidth of the WSS as compared
to an amount of usable bandwidth when using a SMF, thereby
negating, at least partially, the increased fiber transmission
capacity gained by use of FMF.
However, even in a case where such degradation may be reduced, use
of the FMF with the WSS may lead to an increased switching angle
requirement for a switching element of the WSS (e.g., when
maintaining a typical WSS port spacing). For example, for a typical
WSS that includes a set of SMFs (e.g., an input SMF and a pair of
output SMFs) in a linear arrangement, the switching element of the
WSS should be capable of switching between any pair of SMFs. A
solution aimed to reduce degradation of spectral resolution when
using FMF may include a WSS designed to operate based on sampling
modes of N-mode FMFs and coupling each mode of each fiber to a
separate SMF to create a linear structure of individual SMFs.
FIG. 1 is a diagram of a prior WSS designed to reduce degradation
of spectral resolution when using FMF. As shown in FIG. 1, the
prior WSS may include a front-end unit that includes an array of
N-mode FMFs (FMF 1 through FMF M) and a set of mode converters
(mode converter 1 through mode converter M), each associated with a
FMF. As further shown, the prior WSS may include a focusing lens
and a switching element. In practice, the prior WSS may include one
or more additional optical components associated with performing
wavelength selective switching that, for purposes of clarity, are
not shown in FIG. 1. Any FMF may be used as an input and/or an
output.
As shown in FIG. 1, the FMFs may be round FMFs, where each FMF is
capable of supporting N modes. The N modes supported by a FMF are,
collectively, multi-mode in both a first dimension (e.g., a
wavelength dispersion dimension) and a second dimension (e.g., a
switching dimension).
For the prior WSS, a mode converter may be configured to convert a
mode structure of an optical signal to and/or from the multi-mode
structure associated with a FMF 210, from and/or to a set of
single-mode waveguides. Such a device is sometimes referred to as a
"photonic lantern." For example, as shown in FIG. 1, assume that
FMF 1 is an input FMF that supports N modes (e.g., three modes are
used as an example in FIG. 1). The mode converter 1 has at the
right facet in FIG. 1 a set of N single-mode waveguides. At a first
facet of mode converter 1 (e.g., a facet coupled to FMF 1 at a left
side of mode converter 1 in FIG. 1) the N waveguides formed within
mode converter 1 may be brought close together or even touching or
overlapping, such that the N waveguides of mode converter 1 sample
the N modes of the optical signal provided to mode converter 1 via
FMF 1. The N single-mode waveguides then each carry a portion of
the N modes of the optical signal from FMF 1, however the content
of each waveguide may be a linear combination of some or all of the
N modes propagating in FMF 1. For example, the first waveguide may
contain only signal from the first mode of FMF 1, or it may contain
only signal from the second mode of FMF 1, or only signal from the
third mode of FMF 1, or it may contain a combination of signals
from any two or all three modes that were propagating in FMF 1.
However, since each waveguide contains a different combination of
the modes from FMF 1, it is possible by examining the signals
present in all N waveguides to reconstruct the original signals
propagating in FMF 1. In this description we will refer to the
signal coupled to the first waveguide as the "first broken-out
mode," the signal coupled to the second waveguide as the "second
broken-out mode," and so on, understanding that the broken-out
modes may not correspond to distinct modes present in FMF 1. The
number of broken-out modes usually corresponds to the number of
modes present in FMF 1, however there could be situations where the
number of broken-out modes is less than or greater than the number
of modes in FMF 1.
Within mode converter 1 (e.g., moving from left to right in FIG.
1), the set of N waveguides may be formed such that ports at a
second facet of mode converter 1 (shown as a right side of mode
converter 1 in FIG. 1) are arranged in a linear arrangement (e.g.,
a 1.times.3 arrangement is shown in FIG. 1). As shown, other mode
converters of the prior WSS may be similarly configured such that M
sets of N single-mode optical signals, each corresponding to a
different mode converter, are positioned in linear arrangement that
is single mode in the wavelength dispersion dimension and
multi-mode in the switching dimension. Here, since the linear
arrangement of the M sets of N single-mode optical signals shown in
FIG. 1 is single mode in the wavelength dispersion dimension,
degradation of spectral resolution in the prior WSS is decreased
(e.g., as compared to a prior WSS that directly uses a FMF that is
multi-mode in two dimensions, without mode converter).
As further shown in FIG. 1, in order to avoid crosstalk between
wavelength channels associated with each waveguide, the prior WSS
maintains a port spacing (e.g., a distance between adjacent ports)
of typically 4.omega., where .omega. is a beam radius of a
single-mode input. However, the 4.omega. port spacing may result in
an optics height that is undesirably large, which may negatively
impact complexity and/or cost associated with the prior WSS 100.
For example, as shown in FIG. 1, an optics height of the prior WSS
with a quantity of M N-mode FMFs may be determined as follows:
Optics
Height=M.times.((N-1).times.4.omega.)+(M-1)(4.omega.)+2.omega.
As shown in FIG. 1, for a prior WSS including three, three-mode
FMFs (M=3, N=3), and maintaining the port spacing of 4.omega., the
optics height of the prior WSS is approximately equal to 34.omega.
(e.g.,
3.times.((3-1).times.4.omega.)+(3-1)(4.omega.)+2.omega.=34.omega.).
The optics height of a FMF WSS may be reduced, without affecting
performance, using techniques described below, which may reduce
complexity and/or cost of the FMF WSS.
Moreover, with regard to the prior WSS, the switching element must
be capable of switching between (M-1) N ports (e.g., from a port
associated with a first broken-out mode of the first FMF to a port
associated with the first broken-out mode of the third FMF) in
order to achieve switching between any mode of any pair of FMFs.
Switching across a higher number of ports (e.g., across (M-1)N
ports for the prior WSS as compared to (M-1) ports for a SMF WSS)
necessitates an increased switching angle of the switching element
(e.g., as compared to a SMF WSS), which results in increased cost
and/or increased complexity of the switching element.
A potential solution to avoid both the wavelength resolution
degradation issue and the increased switching angle issue is to
sample and reformat the modes of the FMFs into a linear structure
that groups single-mode waveguides corresponding to a particular
broken-out mode (sometimes referred to as "remapping"). For
example, according to the remapping technique, the WSS is designed
to operate based on sampling the modes of each FMF into a linear
arrangement of individual single-mode waveguides, where a first set
of three adjacent single-mode waveguides corresponds to the first
broken-out modes from each FMF, a second set of three adjacent FMFs
corresponds to the second broken-out modes from each FMF, a third
set of three adjacent FMFs corresponds to the third broken-out
modes from each FMF, and so on. In other words, the modes are
remapped to be grouped based on broken-out mode, rather than being
grouped by FMF (as with the prior WSS of FIG. 1).
Use of the remapping technique may reduce the wavelength
degradation and, since ports corresponding to a same broken-out
mode are grouped, will reduce the switching angle requirement for
the switching element of the WSS where a particular broken-out mode
from one fiber couples to the same broken-out mode of another
fiber. However, use of the remapping technique may call for an
undesirable port spacing requirement between ports of the WSS. For
example, since broken-out modes are interleaved as a result of
applying the remapping technique (e.g., such that adjacent
single-mode ports do not correspond to a same FMF), the typical
port spacing of 4.omega. may need to be maintained in order to
avoid crosstalk from an intended fiber to an unintended fiber. As
described above, such a port spacing is directly related to an
optics height of WSS, which may impact complexity, cost, and/or
manufacturability of the WSS.
Implementations described herein provide a WSS, for use with FMF,
that provides decreased degradation of spectral resolution in the
WSS (e.g., as compared to a prior WSS that directly uses a FMF that
is multi-mode in two dimensions) while allowing for a reduced
switching angle requirement and/or a reduced optics height (e.g.,
as compared to a prior WSS that uses SMFs or single-mode waveguides
to carry individual broken-out fiber modes).
FIG. 2A is a diagram of an example WSS 200 for use with FMF (herein
referred to as WSS 200) that provides decreased degradation of
spectral resolution while allowing for a reduced switching angle
requirement and/or a reduced optics height, as described
herein.
As shown in FIG. 2A, WSS 200 may include a front-end unit 205 that
includes an array of N-mode FMFs 210 (FMF 210-1 through FMF 210-M)
and a set of mode converters 215 (mode converter 215-1 through mode
converter 215-M), each associated with a FMF 210. As further shown,
WSS 200 may include a focusing lens and switching element 230. In
practice, WSS 200 includes one or more additional optical
components associated with performing wavelength selective
switching (such as wavelength dispersion means) that, for purposes
of clarity, are not shown in FIG. 2A. Additional description
regarding elements, components, and an environment of WSS 200 are
described below with regard to FIGS. 3 and 4.
As shown in FIG. 2A, in some implementations, FMFs 210 may be round
FMFs, where each FMF 210 is capable of supporting N modes. The N
modes supported by FMF 210 are, collectively, multi-mode in both a
first dimension (e.g., a wavelength dispersion dimension) and a
second dimension (e.g., a switching dimension).
In some implementations, mode converter 215 may be configured to
convert a mode structure of an optical signal to and/or from the
multi-mode structure associated with FMF 210. For example, as shown
in FIG. 2A, assume that FMF 210-1 is an input FMF that supports N
modes (e.g., three modes are used as an example in FIG. 2A). Here,
a first facet of mode converter 215-1 (e.g., a facet coupled to FMF
210-1 at a left side of mode converter 215-1 in FIG. 2A) may
include N ports corresponding to a set of N waveguides formed
within mode converter 215-1. The N ports may be arranged in a
pattern (e.g., a triangular pattern, a circular pattern, a
rectangular pattern, a square pattern, an overlapping pattern,
etc.) such that the N waveguides of mode converter 215-1 sample the
N modes of the optical signal provided to mode converter 215-1 via
FMF 210-1. Here, the N waveguides act as a set of N individual
SMFs.
Within mode converter 215-1 (e.g., moving from left to right in
FIG. 2A), the set of N waveguides may be formed such that ports at
a second facet of mode converter 215-1 (shown as a right side of
mode converter 215-1 in FIG. 2A) are arranged in a 1.times.N linear
arrangement (e.g., a 1.times.3 linear arrangement is shown in FIG.
2A). As shown, the 1.times.N linear arrangement of the N optical
signals at the second facet of mode converter 215-1 is single mode
in the wavelength dispersion dimension and multi-mode in the
switching dimension. As shown, other mode converters 215 of WSS 200
may be similarly configured such that M sets of N single-mode
optical signals, each corresponding to a different mode converter
215, are positioned in a linear arrangement that is single mode in
the wavelength dispersion dimension and multi-mode in the switching
dimension. Here, since the linear arrangement of the M sets of N
single-mode optical signals shown in FIG. 2A is single mode in the
wavelength dispersion dimension, degradation of spectral resolution
in WSS 200 is decreased (e.g., as compared to the prior WSS that
directly uses a FMF that is multi-mode in two dimensions).
As further shown in FIG. 2A, in some implementations, a port
spacing at the second facet of mode converter 215 may be reduced
(as compared to the prior WSS described in connection with FIG. 1).
For example, as described above for the prior WSS of FIG. 1, a
minimum port spacing (e.g., 4.omega.) may be maintained in order to
prevent crosstalk between ports associated with different
broken-out modes of a given FMF. However, with regard to WSS 200,
the N optical signals, associated with a given mode converter 215,
support wavelength channels having the N modes of a single FMF 210.
Since crosstalk among the N modes of a particular wavelength
channel may already be occurring in a FMF core external to WSS 200,
crosstalk within WSS 200 between the broken-out modes of the
particular wavelength channel for a same FMF 210 may not have an
adverse consequence on the performance of the WSS 200. Thus, as
shown in FIG. 2A, the spacing (labeled "d" in FIG. 2A) may be
reduced (i.e., to be less than 4.omega.) between ports at the
second facet of mode converter 215. For example, the port spacing
may be approximately 2.omega. or less. Notably, as shown, the
4.omega. port spacing may be maintained between ports associated
with different FMFs 210 in order to prevent crosstalk.
Here, the reduced port spacing in the switching dimension allows
for a reduced switching angle requirement for switching element 230
and/or a reduced optics height of WSS 200 (e.g., as compared to the
prior WSS described in connection with FIG. 1). For example, as
shown in FIG. 2A, an optics height of WSS 200 with a quantity of M
N-mode FMFs 210 may be determined as follows: Optics
Height=M.times.((N-1).times.d)+(M-1)(4.omega.)+2.omega. As shown in
FIG. 2A, for WSS 200 including three, three-mode FMFs 210, and
using a port spacing of 2.omega. (M=3, N=3, d=2.omega.), the optics
height of WSS 200 is approximately equal to 22.omega. (e.g.,
3.times.((3-1).times.2.omega.)+(3-1)(4.omega.)+2.omega.=22.omega.).
Here, the optics height of WSS 200 (20.omega.) is less than the
optics height of the prior WSS of FIG. 1 (34.omega.), which allows
WSS 200 to be smaller in size and/or less costly to manufacture
than the prior WSS of FIG. 1. Furthermore, due to the reduced
optics height, a switching angle requirement of WSS 200 may be less
than a switching angle requirement of the prior WSS of FIG. 1,
which allows for a less complex and/or less costly switching
element 230 to be utilized in WSS 200.
FIG. 2B is a diagram of an additional example WSS 250 for use with
FMF (herein referred to as WSS 250) that provides decreased
degradation of spectral resolution while allowing for a reduced
switching angle requirement and/or a reduced optics height, as
described herein.
As shown in FIG. 2B, WSS 250 may include a front-end unit 205
including an array of FMFs 210 (FMF 210-1 through FMF 210-M) and a
set of mode converters 215 (mode converter 215-1 through mode
converter 215-M), each associated with a FMF 210. As further shown,
WSS 250 may include a focusing lens and switching element 230. In
practice, WSS 250 includes one or more additional optical
components associated with performing wavelength selective
switching (such as wavelength dispersion means) that, for purposes
of clarity, are not shown in FIG. 2B. Additional description
regarding elements, components, and an environment of WSS 250 are
described below with regard to FIGS. 3 and 4.
As shown in FIG. 2B, in some implementations, FMFs 210 may be round
FMFs, where each FMF 210 is capable of supporting N modes. The N
modes supported by FMF 210 are, collectively, multi-mode in both a
first dimension (e.g., a wavelength dispersion dimension) and a
second dimension (e.g., a switching dimension).
As described above, in some implementations, mode converter 215 may
be configured to convert a mode structure of an optical signal to
and/or from the multi-mode structure associated with FMF 210. For
example, as shown in FIG. 2B, assume that FMF 210-1 is an input FMF
that supports N modes. Here, the first facet of mode converter
215-1 (e.g., a facet coupled to FMF 210-1 at a left side of mode
converter 215-1 in FIG. 2B) may include N ports corresponding to a
set of N waveguides formed within mode converter 215-1. Here, the N
ports may be arranged in a pattern such that the N waveguides of
mode converter 215-1 sample the N modes of the optical signal
provided to mode converter 215-1 via FMF 210-1.
Within mode converter 215-1 (e.g., moving from left to right in
FIG. 2B), the set of N waveguides may be formed such the N
waveguides merge to form a single (e.g., rectangular) waveguide
with a single port at a second facet of mode converter 215-1 (shown
as a right side of mode converter 215-1 in FIG. 2B). The single
waveguide formed from the multiple waveguide provides a 1.times.N
port at the right facet of mode convertor 215-1. Here, the single
waveguide, and the associated port, support an N-mode optical
signal that is single mode in the wavelength dispersion dimension
and multi-mode in the switching dimension. In some implementations,
a height of the port in the switching dimension may be equal to
approximately 1.3.omega..times.(N-1)+2.omega. in order to support
the N modes, while a width of the port in the wavelength dispersion
dimension may be approximately 2.omega. to support a single mode
(i.e., the width of the port may be approximately equal to a
diameter of the single mode). Put another way, the waveguides may
merge to form a single waveguide that supports N optical signals
within a 1.times.N mode structure. Put still another way, space
between the waveguides may be reduced until there is no space
between the waveguides, thereby forming a single waveguide and an
associated single port, where the single waveguide and the single
port are capable of supporting the N optical signals with the
1.times.N mode structure. As described above, crosstalk between the
N optical signals associated with N modes of a particular FMF 210
may not adversely affect performance of WSS 250, which allows any
spacing maintained between the N optical signals, associated with a
given FMF 210, to be eliminated.
As shown, other mode converters 215 of WSS 250 may be similarly
configured such that a set of M N-mode optical signals, each
corresponding to a different mode converter 215, are positioned in
linear arrangement that is single mode in the wavelength dispersion
dimension and multi-mode in the switching dimension. Here, since
the linear arrangement of the set of M N-mode optical signals shown
in FIG. 2B is single mode in the wavelength dispersion dimension,
degradation of spectral resolution in WSS 250 is decreased (e.g.,
as compared to the prior WSS that directly uses a FMF that is
multi-mode in two dimensions, without mode converters).
As further shown in FIG. 2B, in some implementations, an optics
height of WSS 250 may be reduced (as compared to the prior WSS
described in connection with FIG. 1). For example, as shown in FIG.
2B, since mode converter 215 includes a single port with a height
of 1.3.omega..times.(N-1)+2.omega., the optics height of WSS 250
may be reduced. In such a case, the additional waveguide size per
additional mode, associated with a given FMF 210 of WSS 250, may be
approximately 1.3.omega. (where .omega. is the beam radius of a
single-mode input with the same numerical aperture, or far-field
divergence angle, as the multi-mode input). Notably, as shown, the
4.omega. port spacing may be maintained between ports associated
with different FMFs 210 in order to prevent crosstalk.
Similar to WSS 200, the reduced port spacing in the switching
dimension allows for a reduced switching angle requirement for
switching element 230 and/or a reduced optics height of WSS 250
(e.g., as compared to the prior WSS described in connection with
FIG. 1). For example, as shown in FIG. 2B, an optics height of WSS
250 with a quantity of M N-mode FMFs 210 may be determined as
follows: Optics
Height=M.times.[1.3.omega..times.(N-1)]+(M-1)(4.omega.)+2.omega. As
shown in FIG. 2B, for WSS 250 including three, three-mode FMFs 210
(M=3, N=3), the optics height of WSS 250 is approximately equal to
17.8.omega. (e.g.,
3.times.[1.3.omega..times.(3-1)]+(3-1)(4.omega.)+2.omega.=17.8.omega.).
Here, the optics height of WSS 250 (17.8.omega.) is less than the
optics height of the prior WSS of FIG. 1 (34.omega.), which allows
WSS 250 to be smaller in size and/or less costly to manufacture
than the prior WSS of FIG. 1. Furthermore, due to the reduced
optics height, a switching angle requirement of WSS 250 may be less
than a switching angle requirement of the prior WSS of FIG. 1,
which allows for a less complex and/or less costly switching
element 230 to be utilized in WSS 250. Further, an optics height of
a given 1.times.N mode structure of WSS 250 (e.g., associated with
a given mode converter 215) is approximately equal to
1.3.omega..times.(N-1)+2.omega..
The number and arrangement of components shown in FIGS. 2A and 2B
are provided as examples. In practice, WSS 200 and/or WSS 250 may
include additional components, fewer components, different
components, differently formed components, differently designed
components, or differently arranged components than those shown in
FIGS. 2A and 2B. Additionally, or alternatively, a set of
components (e.g., one or more components) of WSS 200 and/or WSS 250
may perform one or more functions described as being performed by
another set of components of WSS 200 and/or WSS 250.
For example, while mode converter 215, associated with WSS 250, is
described as including, at a first facet of mode converter 215
(e.g., a facet coupled to FMF 210), a set of N ports and an
associated set of N waveguides, in some implementations, mode
conversion may be achieved using a different technique. For
example, mode converter 215 may, at the first facet, include a
single port, and a single associated waveguide, that supports N
modes (e.g., a square, circular, or rectangular waveguide that
supports multiple modes in the switching dimension and multiple
modes in the wavelength dispersion dimension). In this example, one
or more sides of the waveguide may, along a length of mode
converter 215 (e.g., moving from left to right in FIG. 2B) rotate,
distort, angle, shift, or otherwise be altered to form the
waveguide that supports the N-mode optical signal that is single
mode in the wavelength dispersion dimension and multi-mode in the
switching dimension. In some implementations, such an arrangement
that does not separate the N modes may provide for a reduced amount
of insertion loss.
As another example, mode converter 215 may include a series of
diffractive elements that convert an N-mode optical signal that is
multi-mode in the wavelength dispersion dimension and the switching
dimension to and/or from an N-mode optical signal that is single
mode in the wavelength dispersion dimension and multi-mode in the
switching dimension.
As still another example, while the optical signals shown in FIGS.
2A and 2B are in a linear arrangement with 4.omega. separation
between sets of optical signals associated with different FMFs 210,
in the switching dimension, in some implementations, the sets of
optical signals may be arranged in another manner. As a particular
example, in some implementations, WSS 200 and/or WSS 250 may be
designed such that sets of optical signals are separated by
4.omega. in the wavelength dispersion dimension. In other words,
the arrangement may be a stacked arrangement rather than the linear
arrangement shown in FIGS. 2A and 2B, in which case the switching
element steers sub-beams in the wavelength dispersion
dimension.
In some implementations, mode converter 215 is optional. FIG. 2C is
a diagram of an another example WSS 275 for use with FMF (herein
referred to as WSS 275) that provides decreased degradation of
spectral resolution while allowing for a reduced switching angle
requirement and/or a reduced optics height, as described herein,
without mode conversion.
As shown in FIG. 2C, WSS 275 may include FMFs 210 that receive
and/or provide N-mode optical signals that are single mode in the
wavelength dispersion dimension and N-mode in the switching
dimension. Such FMFs may be utilized when, for example, mode
conversion is performed at a point on an optical path that is
external to WSS 275, when a transmission fiber is single mode in
the wavelength dispersion dimension and N-mode in the switching
dimension, or the like. In this case, FMFs 210 of WSS 275 may be
capable of receiving and/or providing optical signals that are
single mode in the wavelength dispersion dimension and N-mode in
the switching dimension (i.e., FMFs 210 may be rectangular few mode
fiber, rather than circular few mode fiber). As shown in FIG. 2C,
mode conversion is not necessary within WSS 275 and, therefore, WSS
275 does not include mode converters 215. However, as shown, the
optics height of WSS 275 may be similar to that of WSS 250.
The number and arrangement of components shown in FIG. 2C are
provided as examples. In practice, WSS 275 may include additional
components, fewer components, different components, differently
formed components, differently designed components, or differently
arranged components than those shown in FIG. 2C. Additionally, or
alternatively, a set of components (e.g., one or more components)
of WSS 275 may perform one or more functions described as being
performed by another set of components of WSS 275.
FIG. 3 is a diagram of example components of WSS 300. WSS 300 may
correspond to WSS 200, WSS 250, and/or WSS 275. In some
implementations, WSS 300 may include front-end unit 205 with an
array of FMFs 210, and (optionally) one or more mode converters
215, and lens 217. As further shown, WSS 300 also includes a
reflector 220, a dispersion element 225, and a switching element
230. The tallest component in WSS 300 is typically the reflector
220; whereas we have been previously referring to "optics height"
as the height of the ports and/or modes within front end unit 205,
the height of reflector 220 is equal to or greater than that
"optics height" times the ratio of focal length of reflector 220 to
the focal length of lens 217. So the overall height of WSS 300 is
directly related to the "optics height" previously calculated, and
any increase or decrease in "optics height" corresponds to a
proportional increase or decrease in height of WSS 300.
As described elsewhere herein, WSS 300 may include a wavelength
selective switch capable of providing reconfigurable
wavelength-dependent switching. In some implementations, WSS 300
may be capable of switching a first wavelength channel (e.g. all
modes of the first wavelength channel) to a first optical fiber
while simultaneously switching a second wavelength channel (e.g.
all modes of the second wavelength channel) to a second optical
fiber. In some implementations, WSS 300 may include a set of ports
associated with sending and/or receiving an optical signal. In some
implementations, WSS 300 may be connected to a FMF 210 (e.g., as an
input, as an output). In some implementations, WSS 300 may be
connected to one or more other WSSs 300 and/or one or more other
devices (e.g., receiver modules, transmitter modules) via FMFs
210.
Front-end unit 205 may include one or more components associated
with receiving and/or providing an optical signal via FMF 210
(e.g., a multi-wavelength signal with wavelength channels having N
modes). For example, front-end unit 205 may include a connection
with a set of FMFs 210, a set of micro-lenses, a lens, or the like.
Here, each FMF 210 may transmit an optical signal (e.g., a beam of
light containing, for example, communication signals) into a
respective micro-lens. After passing through the respective
micro-lens, the optical signal may be deflected by the lens and
directed to reflector 220.
In some implementations, front-end unit 205 may optionally include
a mode converter 215. Mode converter 215 may include a component
configured to convert a structure of modes of an optical signal to
and/or from a structure that is single-mode in a first dimension
and multi-mode in a second dimension (i.e., a one-dimensional
structure), as described herein. For example, front-end unit 205
may include mode converter 215 when FMF 210 is a two-dimensional
FMF 210 (e.g., multi-mode in the first dimension and multi-mode in
the second dimension, circular, oval-shaped, etc.), such that mode
converter 215 may convert the mode structure of the two-dimensional
FMF 210 to a structure that is single-mode in a first dimension and
multi-mode in a second dimension.
Reflector 220 may include a component positioned to reflect a beam
of light provided by another component of WSS 300. For example,
reflector 220 may include a spherical reflector positioned to
reflect beams of light from and/or to front-end unit 205,
dispersion element 225, and/or switching element 230.
Dispersion element 225 may include a component positioned to
separate a beam of light into a group of sub-beams (e.g., having
different wavelengths) for transmission (e.g., via reflector 220)
to switching element 230 and/or recombine sub-beams of light for
transmission (e.g., via reflector 220) to front-end unit 205 (e.g.,
to a predetermined input port and/or output port). For example,
dispersion element 225 may include a prism, a diffraction grating,
or the like.
Switching element 230 (sometimes referred to as a modifying
element) may include a component capable of modifying a beam of
light (e.g., a sub-beam provided by dispersion element 225) such
that the beam of light may be switched between optical fibers
associated with WSS 300. For example, switching element 230 may
include a micro-electro-mechanical systems (MEMS) array that
includes a set of movable mirrors, a liquid crystal on silicon
(LCoS) phase modulator array, a liquid crystal polarization
rotating element and birefringent beam steering element, or the
like. In some implementations, a steering angle requirement
associated with switching element 230 may be reduced using the
techniques described herein.
The number and arrangement of components shown in FIG. 3 are
provided as example. In practice, WSS 300 may include additional
components, fewer components, different components, or differently
arranged components than those shown in FIG. 3. Additionally, or
alternatively, a set of components (e.g., one or more components)
of WSS 300 may perform one or more functions described as being
performed by another set of components of WSS 300.
FIG. 4 is a diagram of an example environment 400 in which systems
and/or methods described herein may be implemented. As shown in
FIG. 4, environment 400 may include a group of FMFs 210 connected
to a corresponding group of WSSs 300, optical amplifiers 405,
receiver (Rx) modules 410, and transmitter (Tx) modules 425.
As described elsewhere herein, FMF 210 may include an optical fiber
that supports more than one spatial mode supported by a SMF, but
fewer spatial modes than the multiple spatial modes supported by a
MMF. In some implementations, FMF 210 may be used as an input or an
output of WSS 300. In FIG. 4, all input and output FMFs 210 for a
WSS 300 may be included in Front End Unit 205 of FIG. 3.
Optical amplifier 405 may include a component configured to amplify
an optical signal as the optical signal is transmitted over a FMF
210, an optical fiber that connects WSS 300 and Rx module 410,
and/or an optical fiber that connects Tx module 415 and WSS
300.
Rx module 410 may include one or more components associated with
receiving and/or processing an optical signal, such as optical
receivers, waveguides, demultiplexers, splitters, switches, or the
like. Shown is an implementation where three modes of FMF 210 are
separated into three broken-out modes, each of which may travel via
an individual single-mode fiber, and may be a linear combination of
an original input signal in the three fiber modes. Here, following
detection of a given signal associated with a single-mode fiber,
MIMO processing may extract signals corresponding to each of the
three modes, and provide the extracted signals, to a separate
optical receiver. Each optical receiver of Rx module 410 may
operate to convert an input optical signal to an electrical signal
that represents transmitted data. In some implementations, the
optical receivers of Rx module 410 may each include one or more
photodetectors and/or related components to receive respective
input optical signals output by an optical demultiplexer of Rx
module 410, convert the optical signals to a photocurrent, and
provide a voltage output to function as an electrical signal
representation of the original optical signal. With transmission
using FMF, multi-input multi-output (MIMO) processing techniques
may be used to reconstruct the individual signals encoded on the
multiple modes of the FMF.
Tx module 415 may include one or more components associated with
generating and/or providing an optical signal, such as optical
transmitters, waveguides, multiplexers, combiners, switches, or the
like. Each optical transmitter of Tx module 415 may receive one or
more data channels, modulate the one or more data channels with
optical signals, and transmit the one or more data channels as
optical signals. In some implementations, Tx module 415 may include
multiple optical transmitters. In some implementations, each
optical transmitter may be tuned to use an optical carrier of a
designated wavelength.
The number of components and devices shown in FIG. 4 are provided
as an example. In practice, there may be additional components
and/or devices, fewer components and/or devices, different
components and/or devices, or differently arranged components
and/or devices than those shown in FIG. 4. Furthermore, two or more
components/devices shown in FIG. 4 may be implemented within a
single component/device, or a single component/device shown in FIG.
4 may be implemented as multiple, distributed components/devices.
Additionally, one or more of the components/devices of environment
400 may perform one or more functions described as being performed
by another of the one or more components/devices of environment
400.
Implementations described herein provide a WSS, for use with FMF,
that provides decreased degradation of spectral resolution in the
WSS (e.g., as compared to a prior WSS that directly uses a FMF that
is multi-mode in two dimensions) while allowing for a reduced
switching angle requirement and/or a reduced optics height (e.g.,
as compared to a prior WSS that uses SMFs or single-mode waveguides
to carry individual broken-out fiber modes).
The foregoing disclosure provides illustration and description, but
is not intended to be exhaustive or to limit the implementations to
the precise form disclosed. Modifications and variations are
possible in light of the above disclosure or may be acquired from
practice of the implementations.
Even though particular combinations of features are recited in the
claims and/or disclosed in the specification, these combinations
are not intended to limit the disclosure of possible
implementations. In fact, many of these features may be combined in
ways not specifically recited in the claims and/or disclosed in the
specification. Although each dependent claim listed below may
directly depend on only one claim, the disclosure of possible
implementations includes each dependent claim in combination with
every other claim in the claim set.
No element, act, or instruction used herein should be construed as
critical or essential unless explicitly described as such. Also, as
used herein, the articles "a" and "an" are intended to include one
or more items, and may be used interchangeably with "one or more."
Furthermore, as used herein, the term "set" is intended to include
one or more items (e.g., related items, unrelated items, a
combination of related items, and unrelated items, etc.), and may
be used interchangeably with "one or more." Where only one item is
intended, the term "one" or similar language is used. Also, as used
herein, the terms "has," "have," "having," or the like are intended
to be open-ended terms. Further, the phrase "based on" is intended
to mean "based, at least in part, on" unless explicitly stated
otherwise.
* * * * *